1. Field of the Invention
The present invention generally relates to magnetic data storage systems and to sliders used in such systems. More particularly, the invention concerns a method and apparatus for burnishing sliders during, as well as after manufacture and assembly of the system.
2. Discussion of the Related Art
A magnetic data storage system typically comprises at least one magnetic disk with at least one data recording surface having a plurality of concentric tracks for storing data. A spindle motor and spindle motor controller rotate the disk(s) at selected revolutions per minute (RPM) such that at least one read/write transducer can read data from or write data to a recording surface. In most current systems, the transducer is supported by an air bearing slider which has a top surface attached to an actuator assembly via a suspension, and a bottom surface having an air bearing design and pads to provide favorable flying height of the slider. During operation of the magnetic data storage system, the air bearing slider is positioned above the desired data track by an actuator assembly.
Recently, the recording density of magnetic disks has dramatically increased. In order to take advantage of the increased density, the flying height of the magnetic head has been reduced to 0.1 xcexcm or less. In fact, systems using continuous contact sliders, in which the sliders stay in touch with the disk during all aspects of operation, have been proposed. In such contact recording systems, the magnetic heads read and write in contact with the magnetic disk. U.S. Pat. No. 5,041,932 and Japanese Patent Application Laid-open No. H5-114116 disclose magnetic head structures suitable for such contact recording and reproducing, and a method of manufacturing such structures.
However, inherent in the contact recording and reproducing system is the abrasion of the magnetic head and the magnetic disk due to the sliding contact between them. This problem may be reduced by using a carbon material in the contact pad portion of the head, a protective layer on the magnetic disk, a reduced weight magnetic head, a reduced load head, and/or a perpendicular magnetic recording system. Nonetheless, wear, uneven surfaces, and debris intrinsic in these contact slider systems shortens their life.
For this reason, some of the more conventional magnetic storage systems use air bearing sliders that operate in a contact start/stop mode. The slider and transducer are only in contact with the recording surface when the spindle motor is powered down. As the disk begins to rotate, an air flow is generated which enters the leading edge of the slider and flows in the direction of the trailing edge of the slider. The air flow generates a positive pressure on the air bearing surface of the slider, and when enough pressure builds up, lifts the slider above the recording surface. As the spindle motor reaches the operating RPM, the slider is maintained at a nominal flying height over the recording surface by a cushion of air. Subsequently, as the spindle motor spins down, the flying height of the slider drops until the slider is once again in contact with the disk.
However, due to the slider dragging on the disk surface during start and stop operations, these air-bearing systems, the resulting wear (also referred to as wear durability), unevenness, and debris on the disk and slider surfaces severely reduces system life. Moreover, the entire system may xe2x80x9ccrashxe2x80x9d (ie. the system becomes nonfunctional due to damage) if such contact causes damage to a critical part of the disk or slider, or creates debris that becomes caught between the slider and disk or other crucial components. Additionally, protrusions or uneven slider surfaces created by contact may cause read/write errors, further disk wear, and crashes. Similarly, slider/disk contact may cause improper slider flying height due to inadvertent burnishing, buildup of debris on the slider, or changes in the flight characteristics of the slider.
The flying height of the slider transducer head above the disk is critical for mechanical and magnetic performance. Transducer heads flying too high perform poorly magnetically, for example, providing a readback signal with reduced amplitude, a reduced signal to noise ratio and a reduced resolution for bit detection. On the other hand, transducer heads flying too low are more likely to pick up contamination from the disk that will lead to smears on the heads and to an increase of the hazard of head crashes. One approach to circumvent the undesirable issues associated with wear, durability, and improper flying height is to use load/unload technology.
Typical load/unload technology includes a ramp for the slider/suspension assembly at the outer diameter of the disk where the slider is xe2x80x9cparkedxe2x80x9d securely while the spindle motor is powered down. During normal operation, the disk speed is allowed to reach a selected RPM (which may be below the normal operating RPM) before the head is xe2x80x9cloadedxe2x80x9d from the ramp onto the disk. As the slider approaches the disk surface, an air cushion is generated by the disk""s rotation. The slider can also be xe2x80x9cunloadedxe2x80x9d from the disk""s surface onto the ramp. In this manner, the slider is positioned over the disk without substantial contact with the disk surface. By reducing the contact between the slider and the disk surface, the interface life can be increased. Nonetheless, even with the load/unload system""s reduced contact, the system still risks the dangers cited above because there is frequently some slider/disk contact during start and stop, there is always slider/ramp contact when the spindle motor is powered down, and there is a possibility of more harmful contact if a bumpy load or unload occurs.
In order to reduce the risks cited above as well as properly position the slider (transducer) above the disk surface, manufacturers of the systems often burnish the sliders before assembly. For instance, burnishing has been performed during manufacture in order to obtain a thin-film head slider with stable flying characteristics and good running durability. This is accomplished by polishing the medium-facing slider surface, which constitutes the air bearing surface. Such burnishing decreases the flying height of the slider and evens the air bearing surfaces by wearing flat and burning-in the slider""s air bearing surfaces. Similarly, such burnishing or pre-conditioning of the sliders reduces the likelihood of disk or slider damage because the process removes sharp protrusions and rounds sharp comers significantly reducing the stress imparted on to the disk by the slider and vice versa. Japanese Patent Public Disclosure No""s. Sho 60-185272, Sho 63-70918, Hei 2-199614, Hei 2-212057, Hei 2-301014 disclose polishing films and polishing tapes used during manufacture to polish the air bearing surfaces of sliders. Similarly, a method of preliminary burnishing of contact type magnetic heads during manufacture has been proposed in U.S. Pat. No. 5,887,336. Yet, this proposal only addresses burnishing contact type heads by using an non-lubricated area covering the full circumference of the disk during manufacturing or prior to a normal recording and reproducing.
Unfortunately, pre-conditioning contact sliders or air bearing sliders during manufacture can not cure problems that occur as a result of slider/disk contact that happens after manufacture. Furthermore, burnishing of air bearing sliders during manufacturing creates numerous other setbacks. First, because all air bearing sliders are assumed to burnish at about the same rate, those sliders that require significantly less or more burnish time will have degraded flying characteristics due to excessive or insufficient burnishing. Out of a batch of sliders, this portion can be significant. Second, this approach assumes that the burnishing occurs only initially, when the sliders are conditioned during manufacture, when in fact, burnishing might occur as a result of slider disk contact at any time resulting in incorrect flying height. In particular, if additional burnishing occurs, the flying height of the heads may be too high to allow reading of previously written data, resulting in hard read errors. Finally, over burnishing after system assembly utilizing the disk surface can burn through the air bearing pads, exposing harder, rougher, and/or more jagged structure. This will disturb the overall disk surface by causing scratches, debris trails, carbon wear tracks, or other deleterious effects that may cause a crash, impact long term slider flyability, or deter from disk surface life.
Disk drives that crash or are seriously damaged during use are infrequently repaired due to repair costs which usually exceed the value of the drive. Furthermore, expensive data and time can be lost when the drive goes bad.
Therefore, there is a need for the ability to monitor burnishing during manufacture to avoid over or under-burnishing. Similarly, there is a need for the ability to burnish after manufacture to prevent crashes and extend system life by removing uneven surfaces, protrusions, and debris that develop in systems after manufacture. Moreover, the ability to burnish during the life of the system will allow users to repair incorrect slider flying height which will increase system performance and life.
It is a primary object of the present invention to provide means to burnish the slider after manufacture to prevent crashes and extended system life by removing uneven surfaces, protrusions, and debris that develop in systems after manufacture.
Another object of the present invention is to provide means to burnish during the life of the system will allow users to repair incorrect slider flying height which will increase system performance and life.
In accordance with a primary aspect of the present invention a magnetic data storage system comprises a storage disk having a data surface of concentric radial tracks and a burnishing track, means for rotating said disk, and at least one slider having an air bearing surface for air support of said slider over said data surface, wherein said burnishing track is a dedicated track for burnishing said slider.
Another aspect of the present invention is that the burnishing track is segmented into at least one burnishing zone and at least one monitoring.